In order to code an image signal sequence into a coded signal sequence and to reduce the transmitted amount of information of the coded signal sequence, several coding algorithms including a predictive coding system, an orthogonal coding system, and a vector quantization system can be employed in a conventional image coding system. The coded signal sequence is transmitted to a corresponding decoding system through either a transmission line or a transmission path.
In a digital magnetic recording and playback system, the coded signal sequence is recorded onto a magnetic tape using one or more magnetic heads. In order to transmit and record the coded signal sequence with a high efficiency, the amount of information of the coded signal sequence must be controlled. This is especially true in the digital magnetic recording and playback system, since the number of bits corresponding to a predetermined recording unit, e.g., a track or sync block, has to be constantly controlled in order to carry out trick play functions, such as high speed searching of the magnetic tape.
Examples of recording and reproducing techniques for digital VCR are found in the following articles, which are incorporated herein by reference:
"A Study on Trick Plays for Digital VCR," by Yamamitsu et al., THPM 13.2, pp 184-185, IEEE 1991.
"An Experimental Study for a Home-Use Digital VTR," by Yamamitsu et al., IEEE Transactions on Consumer Electronics, Vol. 35, No. 3, Aug. 1989.
"Rate-Constrained Optimal Block-Adaptive Coding for Digital Tape Recording of HDTV," by Wu and Gersho, IEEE Transactions on Circuits & Systems for Video Technology, Vol. 1, No. 1, March 1991 (pp 100-101).
"Adaptive DCT Coding for Home Digital VTR," by Dol et al., GLOBECOM 1988, pp. 1073-1079.
U.S. Pat. No. 4,920,426 discloses a coding system wherein a histogram of discrete cosine transform (DCT) coefficients is obtained, an amount of information is calculated from the obtained histogram, and then DCT coefficients are quantized by selecting one among a plurality of quantization characteristics in response to the calculated values. However, since an estimated number corresponding to the information amount is determined for each block, the total amount of information in one frame of an image signal cannot be predicted during the initial coding stage. In addition, since the amount of information of the coded signal is not fed back, precise calculations of the information amount is difficult. Moreover, when the amount of information in the coded signal exceeds a set transmission rate, data loss is large due to the discarding of excess data. This, of course, results in degradation of the quality of a reproduced image signal.